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0.1 Report on the 12Th Nanoquanta Workshop on Electronic Excitations

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0.1 Report on the 12Th Nanoquanta Workshop on Electronic Excitations 0.1 Report on the 12th Nanoquanta Workshop on Electronic Excitations. Time-Dependent Density-Functional Theory: Advances and Prospects Aussois (France) 18-22 September 2007 SPONSORS NANOQUANTA Network of Excellence ESF Psi k Programme CNRS IdNano ORGANIZERS Valerio OLEVANO (LEPES-CNRS, Grenoble, France) John J. REHR (University of Washington, Seattle, USA) Gian-Marco RIGNANESE (Universit´eCatholique de Louvain, Louvain-la-Neuve, Belgium) Patrick RINKE (Fritz-Haber-Institut, Berlin, Germany) Francesco SOTTILE (Universidad del Pais Vasco, San Sebasti´an,Spain) Ludger WIRTZ (IEMN/ISEN, Villeneuve d’Ascq, France) WEBSITE http://lab-neel.grenoble.cnrs.fr/etsf/nanoquanta-workshop07 1 The workshop gathered 120 participants from leading international theory groups. There were 46 oral presen- tations (23 invited speakers and 23 contributed talks) and 32 posters. The workshop allowed the participants to discuss the advances in the theoretical and computational treatment of optical and dielectric spectroscopy, photoemission spectroscopy and quantum transport in the framework of time-dependent density-functional theory (TDDFT), many-body perturbation theory (MBPT) and non-equilibrium Green’s function (NEGF) theory. Invited speakers from leading international groups gave an in-depth overview of current research activities within these theories and placed recent results into context. Young researchers (Ph.D. students and Post- Docs) also had the opportunity to present their work (more than half of the oral presentations were given by non-permanent researchers). A special emphasis was placed on advances and perspectives in time-dependent density-functional theory. Indeed, the first session presented two review talks on TDDFT and DFT-like methods applied to quantum transport. A particular effort has been done by the two invited speakers to present the arguments in the most pedagogical manner, ad usum of the youngest participants to the workshop. The next session rather focused to new methodologies implemented into TDDFT. Two sessions (Wednesday 19 afternoon) presented applications of TDDFT to complex technologically important systems and discussed also the relevance of commonly used approximations to TDDFT, as well as advances with respect to these approximations. There was also a session presenting advances in TDDFT theory coming from conserving approximations in MBPT and NEGF (Friday 21 late morning). A session (Tuesday 18 afternoon) was devoted to core-electron spectroscopy and in the same session a speaker was invited to present advances obtained into one of the most recent experimental technique, the Resonant Inelastic X-ray Spectroscopy (RIXS), which is going to have in the next years an important role in driving advances within theory. A series of two sessions (Wednesday 19 morning) were completely devoted to quantum transport, which is an emerging field of computer simulations and whose importance is increasing in the MBPT community. Indeed, the Green’s functions formalism at the heart of MBPT is also particularly well suited to describe electronic quantum transport. Currently, it is used both in the Landauer-B¨uttiker approach and in the non-equilibrium Green’s functions (NEGF) theory, also known as Keldysh formalism. Approaches based on TDDFT have also been presented in this session. The analized applications ranged from models to nanostructures, up to biological systems. A session (Thursday 20 morning) was devoted to DFT or density-matrix functional theory approaches toward an exact treatment of the exchange and correlation, while the next one treated carbon based systems, both addressing quantum trasnport properties and also optical and Raman spectroscopy. The GW method has, as usual, received much attention by this meeting. Both self-consistency, all-electron vs pseudopotentials and beyond GW issues were treated, as well as new implementations into localized basis set. Implementations of spin degrees of freedom (Friday 21 morning) and spin-orbit coupling into the Bethe- Salpeter equation and more in general many-body methods, as well as other interesting effects like those due to the electron-phonon (leading up to superconductivity) and the electron-magnon interaction have been presented here and there along the conference. Finally, several presentations have indicated the strongly correlated systems as a new and interesting domain for ab initio excited state theories. Both advances of the theory and new succesful calculations on strongly correlated systems were presented. Very interesting discussions took place on the complementarity of the two methods, TDDFT and NEGF, toward a description of quantum transport properties. It is worth to notice that the state-of-the-art implementations of all the above mentioned ab initio methods into existing numerical codes was presented in this meeting. The poster session gave rise to very interesting discussions. Indeed, wide variety of subjects were being presented and the discussions went well beyond these subjects. The meeting provided an informal atmo- sphere for stimulating discussions between researchers working in this exciting field. New collaborations were initiated following these discussions. The presentations were collected (some are still missing) and are going to be available on the conference website. They will be very useful for both the participants and those people in the field that did not have the opportunity to attend the meeting. In particular, the review talks may also be used as a starting point 2 to enter the field. 3 0.1.1 Programme Monday 17 Tuesday 18 Wednesday 19 09:00 Welcome 09:00 Pantelides 09:05 Gross 09:45 Hannewald 09:50 Burke 10:20 Coffee Break 10:15 Coffee Break 10:50 Marques 10:45 Mostofi 11:20 Castro 11:15 Ness 11:40 Pouillon 11:35 Verstraete 12:00 Lunch 11:55 Lunch 14:30 Palummo 14:30 Côté 15:00 Freysoldt 15:00 Maitra 15:30 Rohlfing 15:50 Coffee Break 15:30 Coffee Break 16:00 Registration 16:20 Braicovich 16:10 Chelikowski 17:00 Nanoquanta 16:50 Soininen 16:40 Grüning Steering Committee 17:20 Fratesi 17:00 Nanoquanta 17:40 Poster Session + General Meeting 18:30 Aperitif 20:00 Welcome Dinner 20:00 Dinner 20:00 Gala Dinner 21:30 I3 ETSF Party Thursday 20 Friday 21 Saturday 22 09:00 Scheffler 09:00 Rödl 09:00 Gatti 09:30 Helbig 09:30 De Fausti 09:30 Martin-Samos 09:50 Bokes 09:50 Schleife 09:50 Luppi 10:10 Coffee Break 10:10 Coffee Break 10:10 Coffee Break 10:40 Lazzeri 10:40 Hellgren 10:40 Andrade 11:10 Zanolli 11:10 van Leeuwen 11:00 Abedi 11:40 Varsano 11:40 Stan 11:20 Farewell 12:00 Lunch 12:00 Lunch 12:00 Lunch 14:30 Pasturel 14:30 Bockstedte 13:15 Departures 15:00 Blase 15:00 Marini 14:30 Nanoquanta 15:20 Ren EU Review 15:30 Coffee Break 15:40 Coffee Break 16:00 Li 16:10 Ferretti 16:20 Gierlich 16:30 Sasioglu 16:40 Nanoquanta 16:50 Nanoquanta IT1, IT9 Meetings Young Reaserchers Meeting 20:00 Dinner 20:00 Dinner 21:30 Nanoquanta Steering Committee 4 0.1.2 Oral Presentations Limitations of present DFT calculations of transport Kieron Burke Departments of Chemistry and Physics, UC Irvine, Irvine, California, USA Abstract I will discuss several distinct reasons for why present DFT calculations of transport, which combine ground-state DFT and the Landauer formula, might be highly inaccurate. (1) Even within the standard approach, common approximate functionals do not include a derivative discontinuity or correct for self-interaction. This can both misalign levels and broaden resonance peaks when a molecule is weakly coupled to leads. (2) In the weak bias limit, one can use Kubo linear response theory to deduce the exact conductance. We find the Landauer formula misses XC field effects, which likely reduce the conductance. (3) For finite bias, several alternative schemes are being constructed that may or may not reduce to the Landauer formula (with XC corrections). All references can be found in the review: arXiv:cond-mat/0703591 (http://chem.ps.uci.edu/∼kieron/dft/) 5 The frequency dependent Sterheimer equation in TDDFT Miguel A. L. Marques Centre for Computational Physics, Department of Physics, University of Coimbra Abstract Often we are interested in the response of an electronic system to a weak perturbing field. These underlie many different spectroscopy tools, and are therefore a window to the quantum mechanical world. It is then of little surprise that a multitude of methods appeared over the years to calculate response properties. In this talk, we look at a very old method: the solution of the Sternheimer equation. It is well known that this is the method of choice when calculating static response, like static polarizabilities, phonon frequencies, etc. Although a perturbative technique, it avoids the use of empty states, has a quite good scaling (N 2) with the number of atoms, and a relatively small prefactor. The Sternheimer method can be trivially extended to frequency dependent perturbations, giving us access to a variety of dynamic responses. The simplest of these is perhaps the dynamic polarizability α. With basically the same effort we can access the first hyperpolarizability β, that is responsible for the processes of second-harmonic generation, optical rectification and Pockles effect. Van der Waals C6 coefficients are obtained by changing the frequency of the perturbing field from real to imaginary. Finally, it is possible to use the solution of the Sterheimer equation to define the linear-response of the electron localization function (lr-ELF) – a quantity that can be used to help understanding electronic excitations in complex systems. All these phenomena are illustrated with benchmark calculations for molecules and clusters. 6 Time-dependent density-functional theory in the real-time domain: a route to non-linear response properties and ab-initio many-electron Optimal Control theory. Alberto Castro and E. K. U. Gross Institut f¨urTheoretische Physik, Freie Universit¨atBerlin Abstract We discuss the current state of the art of the explicitly time-dependent formulation of time-dependent density-functional theory (TDDFT).
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